Oxidation process



April 1, 1958 Filed Nov. 8, 1952 OXIDATION PROCESS AQUEOUS HYDROFSEROXIDE soLu poNs PRODUCT 3 Sheets-Sheet 1 AQUEOUS ALKALI INVENTORS WILL/AM H. SH/FFLER JOHN E SENGER United States Patent 7 OXIDATION PROCESS William H. Shifller, San Francisco, and John F. Senger,

Berkeley, Calif., assignors to California Research Corporatlon, San Francisco, Calif., a corporation of Delaware Application November 8, 1952," Serial'No. 319,578

7 Claims. c1. 260 -610 This invention relates to an improved process for oxidizing' alkyl aromatic hydrocarbons to aralkyl hydroperoxides- More particularly, it relates to a process for oxidiz'ing hydrocarbons having the formula:

R1 Rr'eH tohydrope'roxides having the formula:

R1 RrJl-O H I R, and R in the formulae are lower alkyl groups, i. e., methyl, ethyl, propyl or butyl, and Ar is an aromatic hydrocarbon radical such as phenyl, tolyl, naphthyl, and the like. More, specifically, the invention relates to the oxidation of cumene, cymene, diisopropylbenzene, secondary butylbenzene, isopropylnaphthalene, and the like, to the corresponding hydroperoxides.

Pursuant to the invention, a body of aqueous liquid is maintained inthe lower portion of a reaction zone. A plurality of serially connected oxidation zones having an aggregate cross-sectional area essentially equal to that of the reaction zone is maintained within the reaction zone. The lateral surfaces of the oxidation zones extend well below the surface of the aqueous liquid so that a part of said, surface. constitutes the effective lower boundary of each oxidation zone. A body of solution of the desired hydroperoxide, in an alkyl aryl hydrocarbon of the type above described is maintained in each oxidation zone. A gradientconcentration, of hydroperoxide in the solutions in the several oxidation zones ranging from 1% to 10% by weightin the first zone of the series to a concentration abov e l5% and usuallyiii therange 15% to 40% by weight in the last zone of the series is maintained. A free oxygen-containing gas is passed upwardly through the solutions in the several oxidation zones. The alkyl aryl hydrocarbon is continuously fed into the first oxidation zone of the series and a solution of hydroperoxide in the alkyl aryl hydrocarbon is continuously withdrawn from the last zone of the series. Partially spent free oxygencontaining gas is withdrawn from the upper part of the reaction zone, an aqueous alkali solution is introduced into each oxidation zone, and aqueous liquid is withdrawn from the lower portion of the reaction zone at a rate adapted to maintain said liquid at approximately constant level in said zone.

The alkyl aromatic hydrocarbon feed is contacted with thefree oxygen-containing gas, usually air, in liquid phase at a temperature ordinarily in the range from 200 to 250 F. Lower temperatures may be employed, but the rate at which the hydroperoxide is formed will be reduced. Higher temperatures are avoided because the hydroperoxides exhibit increased instability as temperatures rise, and at temperatures above 250 F. hydroperoxide yields are decreased due to hydroperoxide decomposition and accelerated side reaction rates. Each of the oxidation zones may be operated at about the same temperature; however, it is preferred to maintain a temperature gradient in the several oxidation zones, the temperature varying inversely with the hydroperoxide concentration in the zones. has been'observed that the oxidation rate increases as the hydroperoxide concentration of the solutions increases. Accordingly, the highest temperature is maintained in the first of the serially interconnected oxidation zones into which the fresh alkyl aromatic hydroperoxide feed is introduced, and the lowest temperature is maintained in the last of the serially interconnected oxidation zones in which the hydroperoxide concentration is highest and from which the product solution of hydroperoxide in hydrocarbon is withdrawn.

The oxidation zones are preferably operated under a superatmospheric pressure ranging from about 20 to 200 p. s. i. g. Superatmospheric pressures decrease losses of the alkyl aryl hydrocarbon by evaporation and make possible the maintenance of higher mole ratios of free oxygen to alkyl aromatic hydrocarbon in the several oxidation zones. The residence time of the alkyl aromatic hydrocarbon feed inthe reaction zone is kept as short as possible compatible with reasonable conversion of the alkyl aryl hydrocarbons to the corresponding hydroperoxide to minimize product losses due to side reactions. Ordinarily, the residence time of the alkyl aryl hydrocarbon in each of the oxidation zones is kept within the range from 1 to 3 hours.

The hydroperoxide products are decomposed by acid. The decomposition reaction is rapid and may be violent at high acid concentrations. Organic acids are formed by side reactions during the oxidation of alkyl aromatic hydro carbon. To prevent acid catalyzed decomposition of the hydroperoxide the pH of the oxidation zones is main- ,tained above 3 during the oxidation. The optimum pH with respect to both product stability and oxidation rate varies somewhat depending upon the specific alkyl aromatic hydrocarbon fed to the process, but in all cases the pH will lie in the range from 3 to 10. In the case of curnene the pH of the oxidation zones is kept above 7, and preferably in the range from 7.5 to 10 by continuously introducing an aqueous alkali solution such as sodium hydroxide, sodium carbonate, sodium bicarbonate and the like into each of the oxidation zones. The concentration of the alkali in water is usually in the range from 0.1% to 3% by weight, and preferably in the range from 0.5 to 1.5% by weight. The aqueous alkali is introduced into the reactor in amounts ranging from 0.01 to 1% by volume of the hydrocarbon introduced, ordinarily 0.05 to 0.3% by volume based on the hydrocarbon feed, is

adequate. a

The invention will be better understood upon consideration of the appended drawings.

Figure l is a diagrammatic illustration of an arrangement of apparatus and process flow for the practice of the invention.

Figures 2 to 5, inclusive, are vertical projections of cross-sections of the apparatus shown in Figure l as viewed at vertical positions 2-2, 33, 44 and 55, respectively.

Figure 6 is an alternative arrangement of apparatus and process flow for the practice of the invention.

Figures 7 to 10, inclusive, are vertical projections of the cross-sections at vertical positions '77, 8-8, 99 and 10-10, respectively.

Figure 11 illustrates a third embodiment of the inven I Patented Apr. -1, 1958 by cylindrical shell 20. The reaction zone is divided into four oxidation zones by intersecting plates 21 and 22. As shown in the drawing, these plates do not extend through out the full vertical length of the reaction zone, but are arranged to leave a free gas space at the top of the reaction zone and an undivided open space at the bottom of the reaction zone. Plates 2 1 and 22 divide the reaction zone into quadrantal oxidation zones A, B, C and D as shown in each of the cross-sections. nozzle 23 is disposed above each of the oxidation zones as shown in Figure 1 and in cutaway cross-section Figure 2. These spray nozzles are connected to aqueous alkali manifold line 24. Gas outlet line 25 is provided to remove the spent oxidation gas from the top of the reaction zone. Line 25 leaves the reaction zone above oxidation zone C. The portion of plate 21, lying between oxidation zones A and C, is desirably carried to the top of the reaction zone so that the spent oxidation gas effluent from the liquid in oxidation zones A and B must travel around that extension of plate 21 in order to reach outlet 25 and as the gas follows this course to the outlet opportunity is provided for the settling of droplets of liquid entrained with the gas eiiluent from the liquid phases in these zones. Each oxidation zone is provided with a control cooling coil 26, a heating coil 27 and an emergency cooling coil 28. The passage of cooling water and steam through coils 26 and 27 can normallybe regulated to hold the temperature in each oxidation zone at the desired level. Emergency cooling coil 28 is provided to check any sudden tendency of the temperature to rise above the desired level. The alkyl aryl hydrocarbon feed is introduced into oxidation zone A through line 29 and a solution of hydroperoxide in the alkyl aryl hydrocarbon is withdrawn from oxidation zone D through line 34. The flow of the feed through the several oxidation zones is illustrated in the cross-section shown in Figure 4. The feed enters oxidation zone A through line 29, passes from zone A to zone B through gate 30, is carried from zone B to zone C through line 31 and gate 32, passes from. zone C to zone D through gate 33 and is withdrawn from zone D through line 34 which is protected by bathe 35 to reduce the aqueous alkali content of the withdrawn product. An air distributor 36 is located in the lower portion of each oxidation zone. Each of the air distributors 36 is connected to air manifold line 37. During operation of the reactor, an aqueous phase is maintained in the bottom of the reaction zone. The level 38 of this aqueous phase is above the lower extremities of plates 21 and 22 so that the surface of the aqueous liquid provides the effective lower boundary of each of the oxidation zones. The outlets of the air distributors 36 are preferably above the surface of the aqueous liquid so that the air is introduced directly into the organic phase rather than into the lower aqueous phase. Actually, the outlets of the air distributors may be placed below the surface of the aqueous liquid, if desired. If they are positioned thus, good contact of the high pH aqueous liquid and the organic phase is assured, and the aqueous content of the product withdrawn from oxidation zone D is not much increased. The organic phase in each of the oxidation zones rides on the aqueous phase at the bottom of the reaction zone. Ordinarily the upper boundaries of the organic phases 39 lie well below the tops of plates 21 and 22 so that there is no overflow across these plates from one oxidation zone to the other. The densities of the organic phases in the oxidation zones are greater as the hydroperoxide content of the phases becomes greater. Accordingly, the levels of the top surfaces of the organic phases in the oxidation zones will not be identical, rather the top level will be highest in zone A in which the organic phase is least dense and lowest in oxidation zone D where the organic phase is A spray most dense. It is possible to omit gates 30, 31, 32 and 33 and graduate the levels of the upper parts of plates 21 and 22 from at highest level between zones A and B to a lowest level between zones C and D and permit transfer of the reaction mixture from one zone to the next by overflow. The bottom surfaces of the organic phases in the several zones will not necessarily lie at identical levels because of the effect of the interconnecting gates between the zones. Plates 21 and 22 extend sufficiently below the lowest of these surfaces to prevent mixing of the organic liquids from one zone to another by passing around the lower extremities of plates 21 and 22.

The lower aqueous phase is continuously withdrawn from the bottom of the reaction zone through line 40 and a substantial part of it is returned by pump 41 through line 42 to aqueous alkali inlet manifold line 24 to insure maintenance of the desired high pH. A part of the lower aqueous phase is withdrawn from the system through line 43. Approximately constant level of the lower aqueous phase is maintained by introducing fresh aqueous alkali through line 24 to replace the aqueous material withdrawn through line 43 and carried out of the reactor with the product through line 34.

Figure 6 and the cross-sectional views shown on Figures 7 to 10, inclusive, illustrate an alternative arrangement of apparatus for the practice of the invention. In this arrangement, plates 50, 51 and 52 divide the cylindrical reactor into segments of equal volume. Oxidation zones A, B, C and D are consecutive segments of the cylindrical reactor and a temperature gradient is maintained across them ranging from the highest temperature at A to the lowest temperature at D. The other parts of the apparatus correspond to those shown in Figure 1 and are labeled to conform with the labeling in Figure l, the letter a having been added to the number which corresponds to the part illustrated in Figure 1.

Figures 11 and 12 illustrate another arrangement of apparatus for the practice of the invention and a crosssectional view of the apparatus. The parts are labeled to correspond to the parts shown in Figure l and the numbers are followed by the letter b." The cross-sectional view shown in Figure 12 is a series of vertical projections taken at successively lower levels in oxidation zones A, B, C and D of Figure 11.

Oxidation of cumene to cumene hydroperoxide proceeds smoothly in the apparatus shown in Figure 1 under the following illustrative conditions. The temperatures maintained in oxidation zones A, B, C and D are, respectively, 241 F., 232 F., 226 F. and 223 F. The concentration maintained of cumene hydroperoxide, expressed in percent by weight, maintained in oxidation zones A, B, C and D, is 6.25, 12.5, 18.7 and 25, respectively. Cumene is passed into zone A of the reactor at a rate of 355 parts by weight per hour. The average residence time of the cumene in each oxidation zone is 1.65 hours. Fresh aqueous sodium carbonate having a concentration of 0.5% by weight is introduced into the upper portion of the oxidation zones at the rate of 17 parts by weight per hour, and the aqueous phase in the bottom of the reactor is recycled to the top of the reactor through lines 42 and 24 at the rate of 17 parts by weight per hour. A mixture of cumene and cumene hydroperoxide is withdrawn from oxidation zone D through line 34. The concentration of cumene hydroperoxide in the withdrawn material is 25% by weight. The product stream contains an appreciable amount of water formed during the oxidation and small amounts of organic side reaction products including sodium formate, methyl phenyl carbinol and acetophenone. The cumene hydroperoxide contained in the product stream can be concentrated for use as a Diesel fuel additive, or for conversion to phenol and acetone, by cleavage in the presence of an acid catalyst.

5 We claim: 1. In a process for oxidizing an alkyl aromatic hydrocarbon having the structure in which R and R are lower alkyl groups and Ar is an aryl or alkaryl radical, to form an aralkyl hydroperoxide by contact with a free-oxygen-containing gas, the improvements comprising continuously introducing said hydrocarbon into a body thereof maintained in an oxidation zone, continuously introducing said oxygen-containing gas into a lower portion of said zone and removing it from a point above the body of hydrocarbon in said zone, continuously introducing an aqueous alkaline solutioninto the upper portion of said zone, continuously withdrawing hydrocarbon from said body and passing it into a second body of said hydrocarbon maintained in a contiguous second oxidation zone, the bodies in said contiguous zones being in indirect heat exchange with each' other, introducing gas and aqueous liquid into said second zone as described in the first zone, maintaining a pool of said aqueous solution in the lower portion of said aqueous liquid forming the pool, and withdrawing liquid hydrocarbon from the body maintained in the second oxidation zone.

2. The process of claim 1 wherein the hydrocarbon is cumene.

3. The process of claim 1 wherein the hydrocarbon is Withdrawn from an intermediate portion of the first said body and is passed to an intermediate portion of the second said body.

4. The process of claim 1 wherein said hydrocarbon overflows from the first said body into the second oxidation zone.

5. The process of claim l wherein the aqueous liquid. in said pool is maitained at a pH above seven.

6. The process of claim 1 wherein the temperature in the first zone is maintained higher than the temperature in the second zone.

7. The process of claim 1 comprising a plurality of oxidation zones wherein the hydroperoxide content in said first oxidation zone is within the range of about 1% to about 10% by weight and is about 15% to about 40% by weight in the last zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,632,772 Armstrong et al May 24, 1953 FOREIGN PATENTS 964,006 France Ian. 18, 1950 

1. IN A PROCESS FOR OXIDIZING AN ALKYL AROMATIC HYDROCARBON HAVING THE STRUCTURE 